The present invention relates to an imaging apparatus, and to an automatic exposure controlling method. More specifically, the present invention relates to an imaging apparatus having an automatic exposure function which can photograph a person at an appropriate exposure, even when photographing the person under backlight conditions, and to an automatic exposure controlling method thereof.
In an imaging apparatus such as a digital camera and so on, when photographing a person and so on under backlight conditions, they are generally photographed at an exposure-amount corresponding to a bright background. In this case, the person often comes out darkened in the bright background and can not be recognized clearly. Therefore, in an imaging apparatus having an automatic exposure device, there are techniques which determine an exposure corresponding to a face of a person even under backlight conditions. For example, there is an exposure controlling method such that a face of a person is detected within an image plane, a detected area is regarded as a light metering area, and an exposure is then determined by a light meter test result of the light metering area.
The invention disclosed in Japanese patent publication No. 2003-107555 is one of the exposure controlling methods as described above. Japanese patent publication No. 2003-107555 discloses an imaging apparatus with an automatic exposure function that has an imaging section, a face detector which detects a face of a person from image data obtained by the imaging section, a light metering section which performs a light meter test on the person detected by the face detector as a light metering area, and an exposure controller which calculates an exposure-amount based on a light metering result of the face of the person by the light metering section and performs an exposure control based on the calculated exposure-amount.
According to the invention disclosed in Japanese patent publication No. 2003-107555, an expected effect can be obtained, only when the face detector can accurately detect the face of the person However, for example, when photographing the person under backlight conditions, the face of the person is often darkened in a step of an exposure control before detecting the face of the person. When the face of the person is darkened, it is difficult to detect the face of the person and there may be a possibility that it is hard to adjust the exposure corresponding to the face of the person.
Therefore, there is another approach in which the face of the person can be accurately detected even under backlight conditions. The invention disclosed in Japanese patent publication No. 2004-201228 is one of such innovations, and relates to a face area detection method and to an apparatus thereof. The method is as follows. First, a plurality of light meter tests is performed with a change of conditions. Then, an image in which saturation in a skin-colored area is the highest is chosen from a plurality of images obtained by the plurality of the light meter tests. Thereafter, an area having a skin-colored hue in the image is detected and the obtained skin-colored area thereby is divided by the saturation. A shape recognition is then performed on the divided skin-colored area by the saturation and finally the face area is extracted.
In the face area detection method and the apparatus thereof as disclosed in Japanese patent publication No. 2004-201228, there is an innovation for accurately detecting a face of a person by performing complicated processes such as performing a plurality of light meter tests with a change of conditions, choosing an image in which saturation in the skin-colored area is the highest from a plurality of images obtained by the plurality of the light meter tests and so on. In addition, in Japanese patent publication No. 2004-201228, it is also disclosed that an extracted result of a face area can be used for brightness compensation and so on. Therefore, if the invention disclosed in Japanese patent publication No. 2004-201228 is incorporated in an imaging apparatus, it is possible to presume that a face of a person can be photographed at an appropriate exposure-amount even under backlight conditions. However, the invention disclosed in Japanese patent publication No. 2004-201228, as described above, has to perform complicated processes such as performing a plurality of light meter tests by the time a face area is extracted, analyzing these light meter test results and so on. Therefore, in the invention disclosed in Japanese patent publication No. 2004-201228, there is a problem such that an image processing circuit becomes complex and large and it becomes a cause of a rise in cost, and additionally it takes time to carry out the complicated processes and thereby a perfect shot may be missed.